The present invention is directed to tires for vehicle wheels, and more particularly to tires for motorcycles.
These types of tires must have a very special structure for supporting conditions of usage that are quite different from those to which normal motor vehicle tires are subjected. It is enough, for example, to cite the fact that these tires must be capable of traveling at quite high camber angle, normally 40.degree.-45.degree., but even over 55.degree., as compared to the maximum values of 3.degree. or 4.degree. for usual motor vehicle tires.
Therefore, this requirement involves, for those tires used on motorcycles, the need for having treads that are comparatively wider, or rather more enveloping, than the treads of motor vehicle tires, and with there being a pronounced curvature in the crown, i.e., a pronounced curvature of the tread at the shoulders that is contrary to what is found in other tires, whose treads are more flattened when built to have a reduction in the section-height/section-width ratio, commonly known as the H/C or aspect ratio.
Moreover, a high stiffness is required in the sidewall for the purpose of supporting the vehicle during cornering with these high camber angles, and for conferring to the tire a greater directional capacity and a lateral stability during straightaway running at a high speed.
All these difficulties are pushed to the extreme in the instance of motorcycle tires for racing on roads or tracts, where their performance is exploited to the maximum limit (camber angle up to 56.degree.), i.e., where the tires are always utilized at the threshold of the critical conditions of usage.
For all these reasons, to date tires for motorcycles have only been able to utilize crossed-ply carcasses, i.e., with pairs of cord plies crossed together, at low angular values (20.degree.-30.degree.) with respect to the circumferential direction, since radial carcasses have proved to be absolutely unsuitable because of their excessive lateral instability in addition to the great flexibility of their sidewalls.